Fluid dynamic bearing oil composition for hard disk drive motor

ABSTRACT

There is provided a fluid dynamic bearing oil composition for a hard disk drive motor. The fluid dynamic bearing oil composition includes 0.5 to 1.0 parts by weight of a defoaming agent based on 100 parts by weight of the total composition. The bubbles in the fluid dynamic bearing oil may be removed by adding a small amount of defoaming agent to the fluid dynamic bearing oil composition for a hard disk drive motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No. 10-2011-0084114 filed on Aug. 23, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid dynamic bearing oil composition for a hard disk drive motor, and more particularly to a fluid dynamic bearing oil composition for a hard disk drive motor, capable of allowing air bubbles to be effectively removed therefrom.

2. Description of the Related Art

A magnetic disk drive, such as a hard disk drive (HDD) or the like, that rotates a recording medium and performs the recording and reproduction of data thereon, increasingly has a higher capacitance and a smaller size. Also, a spindle motor used therefor is required to have an extended lifespan, stability, and high precision in terms of vibrations, in order to bear high speeds.

In the spindle motor requiring these characteristics, a fluid dynamic bearing that surrounds a shaft with a gas or liquid, instead of using ball bearings such as those used in a bearing structure according to the related art has been developed.

Fluid dynamic bearing (FDB) oil is an essential component, necessary to allow a fluid dynamic motor to operate in an appropriate manner, and has been variously developed to have appropriate characteristics through the addition of a material, such as an antioxidant, an extreme pressure additive, or the like, to a basic ester-containing oil as a main component, or employing other methods.

Since compounds based on the ester include about 90% or more of the total amount of the FDB oil, they function to determine the fundamental properties of the FDB oil.

There are also a small amount of additive including less than 5% of the overall oil, and such a small amount of an additive mainly perform specific functions, such as, preventing the oxidation of the FDB oil, reducing the amount of high-temperature evaporation, or the like.

The performance of the FDB oil is very important in order to allow the fluid dynamic motor to operate appropriately, and may be heavily influenced by the characteristics of the oil itself.

However, bubbles present in the oil may also have a negative effect on the characteristics and performances of the motor. Therefore, bubbles in the FDB oil need to be removed.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a fluid dynamic bearing oil composition for a hard disk drive motor, and more particularly a fluid dynamic bearing oil composition for a hard disk drive motor, capable of allowing air bubbles to be effectively removed therefrom.

According to an aspect of the present invention, there is provided a fluid dynamic bearing oil composition for a hard disk drive motor including 0.5 to 1.0 parts by weight of a defoaming agent based on 100 parts by weight of the total composition.

The defoaming agent may be at least one selected from the group consisting of silicone-based materials and non-silicone-based materials.

The silicone-based material may be at least one selected from the group consisting of emulsion-type, compound-type, oil-type, and powder-type materials.

The non-silicone-based material may be at least one selected from the group consisting of mineral oils and polyalkylene glycols.

The defoaming agent may include at least one selected from the group consisting of higher fatty alcohols, higher fatty acids, higher fatty acid esters, higher fatty amines, higher fatty acid amides, higher fatty ethers, and silicone oils.

The defoaming agent may be a foam suppressor.

The fluid dynamic bearing oil composition may contain a basic oil having an ester as a main component thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic cross sectional view showing a motor for an HDD, including a fluid dynamic bearing assembly according to an embodiment of the present invention;

FIG. 2 is a graph showing results of foaming powers according to Inventive Examples and Comparative Example of the present invention; and

FIG. 3 is a graph showing results of defoaming powers according to the Inventive Examples and the Comparative Example of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention may be modified in many different forms and the scope of the invention should not be seen as being limited to the embodiments set forth herein. The embodiments of the present invention are provided so that those skilled in the art may more completely understand the present invention. In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like components.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view schematically showing a hard disk drive (HDD) motor including a fluid dynamic bearing assembly according to an embodiment of the present invention.

Referring to FIG. 1, a fluid dynamic bearing oil composition 19 according to the present embodiment of the invention may include 0.5 to 1.0 parts by weight of a defoaming agent based on 100 parts by weight of the total composition.

Hereinafter, the fluid dynamic bearing oil composition according to the present embodiment of the invention will be described, but the present invention is not limited thereto.

In the fluid dynamic bearing 10, without being limited to, for example, as shown in FIG. 1, an oil composition 19 may be provided between the stationary members 12 and 14 and the rotary members 11, 13, and 22 so that a liquid-gas interface may be formed therebetween.

The stationary members may be a sleeve 12 and a cap 14, and the rotary members may be a shaft 11, a thrust plate 13, and a hub 22.

An oil sealing part 16 may be formed between the fixed members 12 and 14 and the rotary members 11, 13, and 22, particularly between the sleeve 12, the thrust plate 13, and the cap 14.

The cap 14 may be a member that is press-fitted from above the thrust plate 13 to thereby allow a lubricating fluid 19 to be sealed between the cap 14 and the thrust plate 13. The cap 14 may include a circumferential groove formed in an outer diameter direction thereof such that the cap 14 may be press-fitted onto the thrust plate 13 and the sleeve 12.

The cap 14 may include a protrusion formed on a lower surface thereof in order to seal the lubricating fluid 19, and this uses a capillary phenomenon and surface tension of the lubricating fluid in order to prevent the lubricating fluid 19 from leaking to the outside at the time of the driving of the motor.

The fluid dynamic bearing oil composition 19 may include a basic oil having an ester as a main component thereof.

The ester-based oil may be, but is not particularly limited to, for example, diesters obtained from reactions of dibasic acid and nonlinear alcohol, carbonic acid ester base oil, aromatic ester-based oil obtained from reactions of aromatic tri-basic acid and non-linear alcohol, polyol esters obtained from reactions of mono-basic acid and polyhydric alcohol, and the like.

The base oils may be used alone, or in a combination of two or more thereof.

According to the present embodiment of the invention, the fluid dynamic bearing oil composition 19 may include 0.5 to 1.0 parts by weight of a defoaming agent based on 100 parts by weight of the total composition.

For a method of removing bubbles in the fluid dynamic bearing oil composition for a hard disk drive motor, a physical method such as heating, decompressing, centrifuging, or the like, and a chemical method, such as the addition of a defoaming agent, may be employed.

According to the present embodiment of the invention, the fluid dynamic bearing oil composition may include 0.5 to 1.0 parts by weight of a defoaming agent based on 100 parts by weight of the total composition, in order to remove bubbles in the fluid dynamic bearing oil composition for a hard disk drive motor.

Due to this, according to the present embodiment of the invention, bubble problems may be easily solved without changing the manufacturing conditions or the manufacturing apparatuses.

The defoaming agent may be at least one selected from the group consisting of a silicone-based material and a non-silicone-based material.

The silicone-based material may be at least one selected from the group consisting of emulsion-type, compound-type, oil-type, and powder-type materials.

The non-silicone-based material may be at least one selected from the group consisting of mineral oils and polyalkylene glycols.

In addition, the defoaming agent may include at least one selected from the group consisting of higher fatty alcohols, higher fatty acids, higher fatty acid esters, higher fatty amines, higher fatty acid amides, higher fatty ethers, and silicone oils.

The defoaming agents may be classified into three kinds, a foam breaker, a foam suppressor, and a defoaming agent.

The foam breaker may combine or break bubbles by penetrating the bubbles from an air layer in the foam which is a bubble aggregate; the foam suppressor may prevent the formation of foam by penetrating bubbles from a liquid side to thereby combine or break the bubbles; and the defoaming agent may allow bubbles to float by penetrating an interface between the bubbles and thereby combining the bubbles.

The foam breaker may be added to the foam that is previously present, and thereby break a film of the foam. Small liquid droplets of the foam breaker, attached to the film of the foam, may first penetrate the film of the foam and expand themselves, so that the foam may be broken.

According to the present embodiment of the invention, for example, the foam suppressor may be added as the defoaming agent, but is not particularly limited thereto.

The foam suppressor may contain a surfactant that is insoluble in water, as a main component thereof. In the case in which a small amount of the foam suppressor is added into the oil, the foam suppressor may exhibit a function of preventing bubbles.

In addition, the function of the foam suppressor may not be deteriorated even with the use thereof for long periods of time, and the promotion of bubbles may be prevented even in the case that the foam suppressor is concentrated.

According to the present embodiment of the invention, the fluid dynamic bearing oil composition for a hard disk drive motor may contain 0.5 to 1.0 parts by weight of the defoaming agent based on 100 parts by weight of the total composition.

When the defoaming agent is added in an amount of below 0.5 parts by weight, the effect of removing bubbles from the fluid dynamic bearing oil for a motor for a hard disk drive may be insufficient. When the defoaming agent is added in an amount above 1.0 parts by weight, properties of the fluid dynamic bearing oil for a motor for a hard disk drive may be deteriorated due to addition of excessive amount of the defoaming agent.

According to the present embodiment of the invention, the fluid dynamic bearing oil composition 19 for a motor for a hard disk drive may include 0.5 to 1.0 parts by weight of the defoaming agent based on 100 parts by weight of the total composition, so that bubbles in the fluid dynamic bearing oil may be removed, and thus, characteristics and performance of the motor of the hard disk drive may be improved.

Hereafter, the present invention will be described in detail with reference to examples, but is not limited thereto.

According to the examples of the invention, a foaming power and a defoaming power were evaluated in the fluid dynamic bearing oil, by adding a fluid dynamic bearing oil composition containing 0.5 to 1.0 parts by weight of a foam suppressor to an eater based basic oil, in consideration of defoaming effects and economic feasibility.

Specifically, 0.5 parts by weight and 1.0 parts by weight of the defoaming agent were respectively added to the fluid dynamic bearing oil composition for Inventive Examples 1 and 2, and the defoaming agent was not added to the fluid dynamic bearing oil composition for the Comparative Example.

The foaming power and the defoaming power of the oil were measured by using a bubble measuring device. In Inventive Examples 1 and 2 and Comparative Example, 250 ml of each sample was used.

The revolutions per minute (RPM) of the rotor for stirring were 1500 RPM, and the time required for stirring was 10 seconds.

Table 1 below shows a comparison of foaming power among Inventive Examples 1 and 2 and the Comparative Example, while Table 2 below shows a comparison of defoaming power among Inventive Examples 1 and 2 and the Comparative Example.

TABLE 1 Comparative Example Inventive Example 1 Inventive Example 2 Measure- Number of Measure- Number of Measure- Number of ment bubbles ment bubbles ment bubbles 1 0 1 0 1 0 2 0 2 0 2 0 3 0 3 0 3 0 4 59 4 23 4 13 5 89 5 64 5 56 6 119 6 98 6 90 7 164 7 128 7 120 8 192 8 165 8 158 9 202 9 171 9 163 10 214 10 174 10 166 11 211 11 177 11 169 12 219 12 179 12 171 13 219 13 180 13 172 14 218 14 184 14 176 15 217 15 185 15 173 16 217 16 183 16 171 17 218 17 180 17 173 18 218 18 181 18 174 19 217 19 183 19 174 20 217 20 182 20 173 21 217 21 185 21 175

TABLE 2 Comparative Example Inventive Example 1 Inventive Example 2 Measure- Measure- Measure- ment Number of ment Number of ment Number of time (min) bubbles time (min) bubbles time (min) bubbles  0:00 217  0:00 185  0:00 175  1:00 219  1:00 185  1:00 175  2:00 219  2:00 185  2:00 175  3:00 219  3:00 185  3:00 175  4:00 219  4:00 185  4:00 175  5:00 218  5:00 184  5:00 174  6:00 217  6:00 185  6:00 175  7:00 216  7:00 185  7:00 175  8:00 214  8:00 184  8:00 174  9:00 210  9:00 184  9:00 173  1:00 209 10:00 182 10:00 172 11:00 205 11:00 182 11:00 172 12:00 202 12:00 182 12:00 172 13:00 197 13:00 182 13:00 171 14:00 192 14:00 179 14:00 169 15:00 187 15:00 178 15:00 168 16:00 186 16:00 178 16:00 168 17:00 180 17:00 175 17:00 165 18:00 175 18:00 172 18:00 162 19:00 171 19:00 169 19:00 159 20:00 170 20:00 167 20:00 157 21:00 161 21:00 160 21:00 150 22:00 160 22:00 156 22:00 146 23:00 152 23:00 151 23:00 141 24:00 151 24:00 145 24:00 133 25:00 144 25:00 141 25:00 131 26:00 141 26:00 136 26:00 127 27:00 137 27:00 130 27:00 119 28:00 133 28:00 125 28:00 116 29:00 130 29:00 122 29:00 112 30:00 126 30:00 120 30:00 108

FIG. 2 is a graph showing results of foaming powers according to Inventive Examples and Comparative Example of the present invention.

FIG. 3 is a graph showing results of defoaming powers according to Inventive Examples and Comparative Example of the present invention.

Referring to Tables 1 and 2, it may be seen that less bubbles were formed in Inventive Examples 1 and 2 for the fluid dynamic bearing oil composition containing the defoaming agent than in the Comparative Example for a fluid dynamic bearing oil composition not containing the defoaming agent.

Further, referring to Tables 1 and 2, it may be seen that the formed bubbles were more rapidly broken in Inventive Examples 1 and 2 for the fluid dynamic bearing oil composition containing the defoaming agent than in Comparative Example for a fluid dynamic bearing oil composition not containing the defoaming agent.

Therefore, it may be seen that less bubbles are formed in the fluid dynamic bearing oil composition for a hard disk drive motor according to the present embodiment of the invention and the generated bubbles are broken more rapidly, by including 0.5 to 1.0 parts by weight of the defoaming agent based on the 100 parts by weight of the total composition.

That is, according to the present embodiment of the invention, a small amount of defoaming agent may be added to the fluid dynamic bearing oil composition for a hard disk drive motor, to thereby remove bubbles from the fluid dynamic bearing oil, and hence characteristics and performance of the motor for a hard disk drive may be improved.

As set forth above, according to embodiments of the present invention, bubbles in the fluid dynamic bearing oil may be removed by adding a small amount of defoaming agent to the fluid dynamic bearing oil composition for a hard disk drive motor.

While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A fluid dynamic bearing oil composition for a hard disk drive motor, comprising 0.5 to 1.0 parts by weight of a defoaming agent based on 100 parts by weight of the total composition.
 2. The fluid dynamic bearing oil composition of claim 1, wherein the defoaming agent is at least one selected from the group consisting of silicone-based materials and non-silicone-based materials.
 3. The fluid dynamic bearing oil composition of claim 2, wherein the silicone-based material is at least one selected from the group consisting of emulsion-type, compound-type, oil-type, and powder-type materials.
 4. The fluid dynamic bearing oil composition of claim 2, wherein the non-silicone-based material is at least one selected from the group consisting of mineral oils and polyalkylene glycols.
 5. The fluid dynamic bearing oil composition of claim 1, wherein the defoaming agent includes at least one selected from the group consisting of higher fatty alcohols, higher fatty acids, higher fatty acid esters, higher fatty amines, higher fatty acid amides, higher fatty ethers, and silicone oils.
 6. The fluid dynamic bearing oil composition of claim 1, wherein the defoaming agent is a foam suppressor.
 7. The fluid dynamic bearing oil composition of claim 1, wherein the fluid dynamic bearing oil composition contains a basic oil having an ester as a main component thereof. 